System and method for strengthening lightweight ceilings

ABSTRACT

The present invention is directed to a method of reinforcing a waffle-structure ceiling having vertical members. The method includes drilling a hole through the vertical members and through a continuous upper layer covering the vertical members. Then, a reinforcing pin is inserted into the hole such that the shear stresses on the vertical member are transferred to the pin.

PRIORITY INFORMATION

The present invention claims priority to Israeli Provisional Patent Applications: 197620 filed Mar. 16, 2009, and 198478 filed Apr. 30, 2009, making reference herein to both in their entirety.

FIELD OF THE INVENTION

The present invention relates to methods of retro-strengthening light-weight ceiling structures to prevent failure thereof, and to reinforced ceilings including such retrofittable strengthening means.

BACKGROUND OF THE INVENTION

In commercial buildings, particularly halls, lecture theatres, display areas such as furniture showrooms, car showrooms and the like, that are fairly extensive, there is a general desire to provide large open spaces without pillars or load bearing walls within the space enclosed. Pillars and the like are considered undesirable as they obstruct visibility, get in the way of activities such as dancing, and since general purpose spaces are subsequently used for specific purposes, often such reinforcements seem to be positioned in locations where they are unsightly or cause obstructions. To some extent, pillars and internal supporting walls within a space can be avoided by vaulted arches, flying buttresses and the like, or by suspending ceilings from above, using tall posts. Such techniques are not practical in many cases, however. The desire to reduce costs during construction can lead to reduced safety factors. Miscalculation of loads can lead to overloading and failure. Supporting pillars, though load-bearing, are sometimes removed by careless constructors, since they are invariably placed in strategic load bearing positions which typically correspond to exactly where not wanted for optimal use of the space.

Minimizing the weight of ceilings, roofs and of the floor-ceilings between the stories of multi-storey buildings is desirable, since they are required to be self-supporting over the distance that they span, and for the same strength, the lighter the floor-ceiling itself is, the more load can be supported thereupon. As with all building projects, there is a desire to minimize the costs of ceiling-floors and roofs, and to make construction as simple as possible.

Such considerations have led to lightweight ceiling constructions comprising supporting members, typically I beams, spanning between load bearing external walls, with lightweight packing between the members, and a lightweight floor spanning between the supporting members.

A beam is a structural element that is capable of withstanding load primarily by resisting bending. The bending force induced into the material of the beam as a result of the external loads, own weight and external reactions to these loads is called a bending moment.

The behavior of beams is described by the Euler-Bernoulli beam theory:

${\frac{\partial^{2}}{\partial x^{2}}\left( {{EI}\frac{\partial^{2}u}{\partial x^{2}}} \right)} = {w.}$

The curve u(x) describes the deflection u of the beam at some position x (recall that the beam is modeled as a one-dimensional object). w is a distributed load, in other words a force per unit length (analogous to pressure being a force per area); it may be a function of x, u, or other variables.

Note that E is the elastic modulus and that I is the second moment of area. I must be calculated with respect to the centroidal axis perpendicular to the applied loading. For an Euler-Bernoulli beam not under any axial loading this axis is called the neutral axis.

Often, u=u(x), w=w(x), and EI is a constant, so that:

${{EI}\frac{^{4}u}{x^{4}}} = {{w(x)}.}$

This equation, describing the deflection of a uniform, static beam, is very common in engineering practice.

Successive derivatives of u have important meanings:

-   -   u is the deflection.

$\frac{\partial u}{\partial x}$

-   -   is the slope of the beam.

${EI}\frac{\partial^{2}u}{\partial x^{2}}$

-   -   is the bending moment in the beam.

${- \frac{\partial}{\partial x}}\left( {{EI}\frac{\partial^{2}u}{\partial x^{2}}} \right)$

-   -   is the shear force in the beam.

Finite element analysis may also be used to understand beam behavior.

U.S. Pat. No. 4,527,372 to Ridgill, titled “High Performance Composite Floor Structure” describes lightweight flooring consisting of I-beams and horizontally disposed corrugated sheets placed on the I-beams and covered with concrete.

With reference to FIG. 1, a prior art, lightweight ceiling 10 is shown. The lightweight ceiling 10 construction consists of periodic, supporting members 12, typically I beams, with a light-weight filler there-between such as sheets of tinplate 14, and perhaps blocks of expanded polystyrene or polyurethane 16 that though lightweight, provides thermal and sound insulation. An upper layer of reinforced concrete 18 is poured over the beams to connect them and to provide a continuous floor surface. Typically, a gridwork of ribbed mild steel reinforcing bars 20, rebar, is constructed, and concrete is poured therearound. To reduce weight, lightweight concrete with ash aggregate may be used.

The load is essentially supported by the flanges 11, 13 of the beam, which are typically in compression and tension respectively. Generally, I-beams are used, consisting of horizontal flanges 11, 13, separated by a web 15, it being appreciated that the loads on such ceiling-floor constructions is supported primarily in upper and lower surfaces. Other types of beams, such as rectangular beams, T beams, C beams and square extrusions are sometimes used (not shown). The separation of the beams 12 is a design factor which depends on the span and expected loadings. Typical separations are 60 cm to 90 cm.

A lower concrete surface 22 may be added as a ceiling. This is typically very thin, as it is often not considered a structural, load bearing element. Nevertheless, this may also be fabricated from reinforced concrete containing reinforcing rods 23. While beams 12 are considered sufficiently strong to endure tensile forces, there has been some concern about their ability to withstand shear stresses.

One type of lightweight ceiling is the waffle structure, which was popular in the Sixties and Seventies.

Another ceiling construction technique that was widely used in Israel between the years 1992 and 2001 is the so-called “PalKal” ceiling, invented by Engineer Eli Ron described in Israel Patent No. 104,101, which is incorporated herein by reference. This ceiling construction method was invented in 1992 and was widely used for general purpose and industrial buildings such as conference centers, shopping centers, showrooms, offices and the like.

Recognizing that for simply spanning structures, the load is carried by the lower and upper surfaces, generally in tension and compression respectively, the PalKal ceiling takes the ideas shown in FIG. 1 a step further.

With reference to FIG. 2, a PalKal structure 110 is shown. In the PalKal approach the concrete lower layer 122, vertical members 112 and upper layer 118 and are each fabricated in situ by casting, avoiding the expense of precision cast factory products beams and the transportation thereof.

As shown in FIG. 3, reinforcement rods 120 and/or a grid are laid down (step 1) and a continuous concrete lower layer (ceiling) 122 is poured theraround (step 2) typically using ready mixed concrete. Whilst the concrete is still wet, an inverted tinplate form 114 is placed periodically over the damp concrete (step 3) and concrete is poured therearound, thereby casting vertical members 112 also known as ribs, web or spacers, making an inverted waffled ceiling structure (step 4). The forms may be substantially square or oblong or may be essentially continuous to provide tunnel like voids, depending on whether the ceiling spans in one or two directions. Sometimes the voids include packing, perhaps polystryrene or polyurethane foam 116, for thermal and/or acoustic insulation. Reinforcing bars 120 may then be laid over the inverted waffled structure in one or more directions, depending on the spanning. Sometimes a preformed grid is used (step 5). An upper concrete layer 118 is then poured thereover (step 6). A floor covering may be added (step 7).

PalKal initially gained popularity as a ceiling/floor technology for large open spaces such as conference halls, display showrooms and banqueting suites, being cheap to construct and apparently adequate.

That was until in May 2001 the Versailles wedding hall in Jerusalem collapsed leading to the death of 23 people and the injury of more than 300 people.

As is often the case in such cases, the tragedy was the cumulative result of a number of decisions and actions. The construction method was never approved by an authorized body and did not meet accepted or established engineering standards. It would appear that reinforcing pillars had been removed. Wiring and the like may have weakened the floor. Both the inventor engineer and other engineers involved in the original construction and in subsequent alternations were found guilty of manslaughter and received prison sentences. This emphasizes the reality of building projects of this nature, where to keep costs and weight as low as possible, the calculated safety factors may be inadequate. Actual construction may be sub-standard, and after building, subsequent decisions to remove pillars or walls may be taken without due consideration. In the Versailles disaster, the collapse occurred when a large number of guests (several hundred) danced in step, setting up harmonic vibrations. The weight of so many guests was not taken into account when the building was constructed.

In the wake of the disaster, other PalKal constructions were deemed unsafe for the usages to which they had been put. It is not just fatigue failure induced by vibrations. Sometimes tremendous weight is inadvertently loaded onto floors not designed to take such high static loads. For example, the Israel Patent Office relocated since they were in a PalKal building and had an enormous number of heavy files leading to a risk of collapse.

PalKal is no longer used, but there were a large number of PalKal constructions including municipal and government buildings, hospital wards, the Hebrew Union College and the like.

It will be appreciated that once built, it is generally preferably to find strengthening methods to renovate and strengthen such buildings where possible, rather than to demolish, and several attempts have been made for so-doing.

It will be appreciated that concrete consists of cement, sand, aggregate, reinforcement and water. Different types and quality of sand may affect the strength of the concrete as can impurities in the water. Strong concrete is formed where it is allowed to dry slowly, or cracks may result. Even where concrete is carefully mixed with exact proportions, the temperature and humidity of the air can and does affect the properties of the resulting concrete. Thus, in Israel, the same recipe may give significantly different results in different areas of the country. Similarly, the strength of concrete may depend on the weather at the time of pouring even where concrete using the same proportions of materials from the same sources is cast in the same location, such as if concrete is poured in summer or winter. Usually, the safety factors are large enough to cover all eventualities, but spanning large areas with lightweight ceilings is a demanding application, where it is imperative to minimize weight. On examination of failed PalKal ceilings it appears that a point of failure is at the base of the vertical members 112 (web), and a cause of failure is inadequate resistance to shear. The vertical members 112 between the forms are generally not reinforced at all, and certainly not at the bases thereof. It takes time to position the forms and the concrete of the lower ceiling layer 122 may have started to harden before the vertical members 112 are poured. There may be a difference in humidity or composition of the concrete between the lower (ceiling) layer 122 and the vertical members 112. This may result from a different batch delivered by a different cement mixer. Residual stresses forming as concrete dries, may result in cracking at or near the junction between the vertical members 112 and the lower ceiling layer 122.

With reference to FIG. 4, a prior art PalKal type structure 110 is shown, consisting of a lower (ceiling) layer 122, periodic, vertical members 112 spanning in one or two directions, and cast around formers 114, with a light-weight filler there-between such as expanded polystyrene or polyurethane 116, over which, an upper floor layer 119 of reinforced concrete consisting of a grid of reinforcing rods 120 covered with concrete 118, mutatis mutandis. A reinforcing structure 25 is retrofitted to strengthen the ceiling 110 and to help the vertical members 112 resist shear. Reinforcing structure 25 consists of reinforcing plates 36 that are appended to the upper layer (floor) 118 and lower layer (ceiling) 122 respectively and bolted together by bolts 34. The bolts 34 are fixed through holes drilled through the lightweight structure between the beams, and the plates 30, 36 take some of the tensile and compressive loads on the vertical member 112 therebetween, and the bolts 34 support the vertical member 112, clamping the outer layers 118, 122 thereto. Additionally, the plates 30, 36 help the floor 118 and ceiling 122 layers take up some of the loading.

In order to install reinforcement structure 25, holes are drilled through the PalKal structure 110 from above or below. Floor covering 170 placed on ceiling 110, such as floor tiles, parquet or carpeting, need to be removed and then replaced. The reinforcement process is therefore very costly. To leave a smooth surface, the plates 30, 36 maybe recessed or counter sunk. This adds additional cost and weakens the upper 118 and lower 122 concrete layers. Although this retrofitting solution has been applied successfully, to reinforce PalKal structures 110, it requires removal of false ceilings and floor coverings 170 to position the plates 30, which have to be covered to provide an aesthetic solution. There is a need for alternative solutions, and the present invention addresses this need.

SUMMARY OF THE INVENTION

A first aspect of the invention is directed to a method of reinforcing a waffle-structure comprising vertical members, around forms between the vertical members and a continuous upper layer covering the vertical members and filler, the method comprising:

drilling a hole through the vertical members and at least partially through the upper layer, and inserting a pin into the hole such that shear stresses on the vertical member are transferred to the pin.

Typically the waffle structure is a Palkal structure and further comprises a continuous lower layer.

Typically, the forms are fabricated from tinplate.

Optionally the forms include a lightweight insulating filler material.

Typically, the lightweight insulating material comprises expanded polymer foam.

Most typically the expanded polymer foam is selected from the list consisting of polystyrene, polyurethane and polypropylene foams.

Optionally, the drilling is from above and the hole passes through the upper layer and into the vertical member.

Optionally the hole passes into a lower layer and is a blind hole.

Optionally, the hole passes through the lower layer and is a through hole.

To transfer the shear stress to the pin, an adhesive is injected into the hole and the stresses are transferred to the pin via the adhesive.

Optionally, the hole is a-through hole and the adhesive is provided in excess such that a blob of adhesive is formed beyond the fur surface from a point of injection.

Alternatively, a plate is threaded over bar to retain adhesive whilst it hardens.

Optionally, the hole is drilled from below and passes through vertical member and into an upper layer covering the beam.

Optionally, the structure comprises a lower layer and the hole is drilled from below, through the lower layer and into the vertical members.

Preferably, the hole is drilled into an upper layer.

Optionally, the hole is a through hole, and is drilled through the upper layer.

Optionally, the method further comprises threading a protruding end of the pin through a metal plate and locking in place.

Optionally, locking comprises welding the pin to the plate.

Alternatively, locking comprises, bending over protruding end of the vertical pin.

Preferably however, the protruding end of the pin is threaded and locking comprises applying a bolt onto the pin.

Usefully, the method further comprises a preliminary step of locating the vertical member.

Optionally, the method of locating the vertical member is selected from the list of visible observance, distance measurement, infra red emittance mapping, vibration mapping and drilling exploratory holes.

A second aspect of the invention is directed to providing a retro-reinforced waffle ceiling structure comprising substantially vertical pins passing through vertical members and at least one external layer of concrete; the pin coupled to the vertical member to combat shear stresses in the vertical member.

Typically, the at least one external layer of concrete includes an upper floor covering the vertical members.

Typically, the at least one external layer of concrete includes a lower layer contacting the undersurface of the vertical members.

Preferably the structure is a PalKal structure comprises both upper and lower layers.

In some embodiments, the said at least one external layer comprises reinforced concrete.

Optionally, the substantially vertical pin comprises a reinforcement bar of mild steel with ribbing coupled to the vertical member by an epoxy.

Typically, a metal plate is positioned over a protruding end of the substantially vertical pin and either the pin is bent over to engage the plate, the pin is welded to the plate or the pin is threaded and a nut is threaded onto the thread.

BRIEF DESCRIPTION OF FIGURES

For a better understanding of the invention and to show how it may be carried into effect, reference will now be made, purely by way of example, to the accompanying Figures, wherewith it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. Thus exemplary non-limiting embodiments of the invention will be described with reference to the following description in conjunction with the figures. Identical structures, elements or parts which appear in more than one figure are labeled with a same or similar number in all the figures in which they appear, in which:

FIG. 1 is a schematic cross-section through a lightweight ceiling of the prior art comprising beams, filler between the beams, a concrete upper layer and a concrete lower layer.

FIG. 2 is a schematic cross-section through a PalKal structure;

FIG. 3 is a flow chart summarizing how the PalKal structure of FIG. 2 is fabricated;

FIG. 4 is a schematic cross-section through one system for reinforcing PalKal in accordance with the prior art;

FIG. 5 is a schematic cross-section through a PalKal structure of FIG. 2 reinforced in accordance with embodiments of the present invention, and

FIG. 6 is a flowchart summarizing methods of reinforcing a lightweight ceiling by adding vertical reinforcement bars positioned through the vertical members.

DESCRIPTION OF THE EMBODIMENTS

With reference to FIG. 1, a prior art, lightweight ceiling 10 is shown. The lightweight ceiling 10 construction consists of periodic, supporting members 12, typically I beams, with a light-weight filler there-between such as sheets of tinplate 14, and perhaps blocks of expanded polystyrene or polyurethane 16, over which, a layer of reinforced concrete is poured 18. Typically, a grid of reinforcing rods 20 is laid down and concrete is poured thereover. The ceiling structure 22 therebeneath may also be fabricated from reinforced concrete. The load is essentially supported by the flanges 11, 13 of the beam, which are typically in compression and tension respectively. Generally, I-beams are used, consisting of horizontal flanges 11, 13, separated by a web 15, it being appreciated that the loads on such ceiling-floor constructions is supported primarily in upper and lower surfaces. Other types of beams, such as rectangular beams, T beams, C beams and square extrusions are sometimes used. The separation of the beams is a design factor which depends on the span and expected loadings. Typical separations are 60 cm to 90 cm.

I beams are generally manufacture in factories to very high tolerances, and may be fabricated from reinforced or pre-stressed concrete, steel or even wood.

The base of the horizontal beam is in tension, and the top is in compression. Despite the asymmetrical loading, many commercially manufactured beams are symmetrically reinforced. Sometimes beams are asymmetrically reinforced with additional reinforcement in the flange intended to be in the lower layer, in tension. In such cases, mounting upside down can cause later failure. If the reinforcement rods in the lower half of the beam, are broken, perhaps whilst drilling thereinto to fix a ceiling support structure thereto, this can also be a cause of failure.

With reference to FIG. 2, a PalKal type ceiling 110 is shown. PalKal type ceiling 110 consists of a lower layer 122 of reinforced concrete; a network of vertical members or web sections 112 around forms 114 that define voids that may be filled with insulation material 116; an upper layer 118 of concrete that binds the PalKal structure together. A floor covering 170 is typically fixed over the upper layer. This may consist of ceramic tiles over a bedding of sand, linoleum, carpet, parquet floor, etc. Ceiling tiles (not shown) may be attached to the lower level, or, more commonly, a false ceiling may be suspended therebeneath.

FIG. 3 shows how a PalKal structure of the prior art is fabricated. Firstly, reinforcement rods are laid down—step 1. Concrete is poured thereover—step 2. Then formers, typically inverted tin-plate boxes 114, perhaps filled with insulating material 116, with rounded corners are placed on the wet concrete 122 and pushed down thereinto—step 3. The forms may be square or slightly oblong, for ceilings designed to span in two directions, or may be tunnel like for single spanning ceilings. Concrete is poured therearound—step 4, thereby forming a structure of vertical members, variously described as webs, ribs or spacers 112. An upper layer of concrete 118 (typically reinforced) is poured thereover—step 5. Once set, a floor covering may then be laid thereover—step 6.

Typically there is no single cause of failure. The ceiling could be under-engineered to reduce weight and costs, with not enough support and structural integrity for designed purpose. It may be overloaded due to unexpected use. Sometimes, load bearing walls or pillars are removed. Generally concrete hardens continuously for many years as complex chemical reactions occur. Sometimes, a crystalline phase transformation results in concrete beams becoming embrittled. Fatigue, i.e. vibration caused weakening is more prevalent in metal structures but is not unknown in concrete. Another cause of failure is the generation of harmonic vibration patterns. It is likely that the vibrations caused by a circle of stomping dancers was a contributory factor in the Versailles disaster.

Essentially though, it has been recognized that PalKal type structures fail in shear, often at the junction where the vertical members and the lower layer meet. Where structures containing such beams are under-engineered for the purpose to which they are put, it is necessary to reinforce the structure at these points to prevent shear failure.

With reference to FIG. 4, a prior art solution for reinforcing a PalKal type structure 10 is shown. PalKal type structure 10 consists of periodic, vertical concrete members 12 spanning in one or two directions and coupling together upper and lower continuous horizontal layers to form a structure often compared to a waffle, around voids that typically defined by tinplate forms that may be filled with a lightweight filler material perhaps blocks of expanded polystyrene or polyurethane 16. A reinforcing structure 25 consisting of reinforcing plates 30, 32 appended to the floor and ceiling respectively and bolted together by bolts 34 is provided. The bolts 34 are easily fixed through drilled holes through the lightweight structure between the beams, and the plates 30, 32 take some of the tensile and compressive loads on the beam, and the bolts 34 support the web 15, helping it resist shear. Additionally, the plates 30, 32 help the upper layer (floor) 19 and lower layer (ceiling) 22 take up some of the loading.

This retrofitting solution has been applied successfully, to reinforce PalKal type ceilings, but it requires removal of false ceilings and flooring materials to position the plates, which have to be covered to provide an aesthetic solution. At least two holes and sometimes a rectangular arrangement of four holes are drilled around the member to be reinforced. Thus for a given density of weak-points to be reinforced, it is required to drill twice or four times as many holes.

With reference now to FIG. 5, a schematic cross sectional view of a PalKal type ceiling 10 in accordance with a first embodiment of the invention is shown.

In contradistinction to other approaches and against intuitive practice, vertical holes are drilled through the vertical members 112 themselves, and reinforcing rods 40 are inserted thereinto. These reinforcing rods are fixed to the vertical members 112 and resist shear, which is the main type of failure of such vertical members 112 in PalKal type ceilings 110.

It is noted that the reinforcing rods 40 are typically bolts or sections of ribbed mild steel reinforcement bars—rebar. In one embodiment 40B, an adhesive, such as an epoxy 50 is extruded into the drill hole to lockingly engage the bolt as the adhesive cures. The end of the bolt may be configured to tap into and engage the concrete floor layer over the beam.

By drilling from below, the carpet, parquet, tiling, linoleum or other floor covering 170 need not be removed or damaged. Access to the lower layer 122, if concealed at all, is often simply an issue of removing a false ceiling therebelow. Occasionally, the lower concrete layer 122 itself is visible from below, but even in such cases, damage caused is easily disguised since such concrete ceilings are usually several meters overhead and are typically painted white.

Within the scope of the invention, are included embodiments drilled from above 40C. Such embodiments are particularly appropriate where the floor is exposed due to renovation or where the ceiling is inaccessible, such as where plastered and painted. Indeed, in some embodiments, the bolt holes may be through-holes 40A, passing through the full thickness of the ceiling and roof, and perhaps engaging counter-sunk nuts 42 or female tapped holes in plates 44 affixed therearound.

In all cases, and in contrast to the prior art, the reinforcing pins 40 fit into holes 60 drilled through the vertical members 112. Generally clearance holes 60 are used, with an adhesive 50 such as epoxy resin used to transfer stress from vertical member to pin 40.

Typically, the pin 40 is a section of rebar; the reinforced bars with ribbing designed for engaging concrete but equally useful for engaging epoxy and the like. The pins may be threaded bolts that self-tap into the vertical member, but such solutions are generally better for combating shear in wooden beams than in concrete ones, as incorporated in PalKal. In one embodiment, the pins are inserted from below 40A and include a self-expanding means such as is used for chandelier bolts, so that the bolt expands to press on the walls of the hole therearound.

To facilitate their drilling, the location of the vertical members 112 may be found by a variety of means. Sometimes their position can be directly observed from below. Sometimes, light fixtures and the like provide an indication. If the plans are available, the position may sometimes be determined by measurement. The coin-tap test, sonar or thermal imaging are other, more sophisticated means of determining the position of the beams. Drilling exploratory holes through the concrete outer layer is a further option.

With reference to FIG. 6, the method of reinforcing a lightweight ceiling comprises the steps of

-   -   (a) locating at least a first vertical member 112;     -   (b) drilling a hole 60 vertically through the vertical member         112;     -   (c) injecting an adhesive-filler 50 such as an epoxy into the         hole 60, and     -   (d) inserting a reinforcing bar or other type of pin 40 through         the hole 60 and allowing the adhesive filler 50 to cure, such         that the adhesive filler 50 transmits shear forces from the         vertical member 112 to the pin 40.

The drilling may be from above or below. The substantially vertical hole 60 may be drilled through either the upper layer 118 or the lower layer 122, and at least into the vertical member 112. In preferred embodiments, where drilled from below, the vertical hole 60 is drilled upwards, through the vertical member 112 and into the upper layer 118. Where drilled from above, the vertical hole is drilled down through the vertical member 112 and into the lower layer 122. It is a particular feature of reinforcement methods of the invention, that by drilling from below, floor coverings 170 such as carpets, tiles, linoleum and parquet do not need to be removed or damaged. Lower ceiling covers, such as false ceilings, insulation tiles, decorations and/or lighting fixtures may be removed if necessary, to allow access to lower surface of the ceiling. Even in embodiments where the hole 60 is a through-hole, the damage to the floor is localized and minimal. A washer plate or 44 and nut 42 may provide appropriate termination.

Generally, it is more convenient to work from below, but where the ceiling is over the uppermost storey, whether being the roof, or covered with a roof, it may be more convenient to work from above.

The drilling of the holes 60 may be performed using any suitable concrete drill, such as any of the drills described in U.S. Pat. No. 7,308,949 to Agehara et al., titled “Concrete Drill”, U.S. Pat. No. 7,001,120 to Moser et al., titled “Drilling Tool”, U.S. Pat. No. 6,719,072 to Bongers-Ambrosius, et al., titled “Suction Drill Unit for Dowel Anchorage in Rock” and U.S. Pat. No. 6,629,805 to Eischeid, titled “Hard Metal Drill Bit for use on a Drill”, the disclosures of all of which are incorporated herein by reference.

For filling the clearance hole 60 and bonding to the vertical member 112 to the pin, an epoxy or one or more of the adhesives described in Canadian patent publication 2 552 929, titled “Composite Materials and Methods of Making the Same” may be used.

In some embodiments of the invention, the adhesive 50 is first injected into the hole 60 and only afterwards is the pin 50 inserted into the hole 60. In other embodiments of the invention, the pin 40 is first inserted into the hole 60 and then the adhesive 50 is injected around the pin 40.

Optionally, the pins 40 may protrude beyond the floor 118, 170 and could be used for anchoring walls thereto or below the ceiling layer 122 for affixing light fittings, air conditioning units or conduits thereonto. Ends of bars 40 are optionally tapped with a screw threading which matches a corresponding inner threading of nuts 42.

Instead of or in addition to bonding the vertical pin 40 to the vertical member 112 via an adhesive 60, a pin having an expanding head may be used, such as described in U.S. Pat. No. 7,494,310 to Bodin et al., titled “Mushrooming Expandable Anchor”, U.S. Pat. No. 4,011,786 to Liebig, titled “Expandable Dowel”, U.S. Pat. No. 5,297,909 to Tsay et al., titled “Self-Drilling expansion Drill” or U.S. Pat. No. 6,921,237 to Vassiliou, titled “Fastener having a Tab in the Contact Region”, the disclosures of all of which are incorporated herein by reference.

Either the top or bottom ends of the pin 40 may be threaded for engaging nuts 42 or threaded locking plates 44. Typically, a plate 44 with a clearance hole 60 therethrough is threaded over the vertical pin 40 and a nut 42 is threaded onto the threaded protruding end of the substantially vertical pin 40.

While the above description relates to installing reinforcement pins 40 from below, without requiring removal of floor tiles or other covering 170, above the reinforced ceiling, the principles of the present invention may be used to install reinforcement pins 40 in a ceiling from above, without requiring access from below. It is also noted that, in some embodiments of the invention, a ceiling may be reinforced from both above and below, for example to speed up the work, while using some or all of the features described above, such as drilling holes 60 within the vertical members 112 and/or use of an adhesive 50.

In contradistinction to the prior art reinforcement method shown in FIG. 4, it will be appreciated that only half the number of holes 60 are required and the disruption to floor coverings 170 in minimal. It will further be appreciated that the method described herein is generally faster to implement and the time that the storey below or above the floor being reinforced is out of use due to the disruption caused by workmen, is minimal.

The same pin and/or installation method may be used throughout an entire reinforced ceiling or different embodiments may be used for different locations on the same ceiling. For example, the specific embodiment to be used may depend on the specification of the beams, such as their strength, size and geometry.

The term pin is used generically to include bars, rods, bolts and the like. The term vertical member includes ribs, spacers, webs, vertical walls of waffle sections and other reinforcing elements that serve the purpose of the web of an I beam. Thus persons skilled in the art will appreciate that the present invention is capable of much variation and is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined by the appended claims and includes variations and modifications of the various features described hereinabove, which would occur to persons skilled in the art upon reading the foregoing description.

In the claims, the word “comprise”, and variations thereof such as “comprises”, “comprising” and the like indicate that the components listed are included, but not generally to the exclusion of other components. 

1. A method of reinforcing a waffle-structure ceiling comprising vertical members, around forms between the vertical members and a continuous upper layer covering the vertical members and filler, the method comprising: drilling a hole through the vertical members and at least partially through the upper layer, and inserting a reinforcement pin into the hole such that shear stresses on the vertical member are transferred to the pin.
 2. The method of claim 1, wherein the ceiling further comprises a continuous lower layer.
 3. The method of claim 1, wherein the forms are fabricated from tinplate.
 4. The method of claim 1, wherein the forms include a lightweight insulating material.
 5. The method of claim 1, wherein the lightweight insulating material comprises expanded polymer foam.
 6. The method of claim 5, wherein the expanded polymer foam is selected from the list consisting of polystyrene, polyurethane and polypropylene foams.
 7. The method of claim 1, wherein the drilling is from above and the hole passes through the upper layer and into the vertical member.
 8. The method of claim 7, wherein the hole passes into a lower layer and is a blind hole.
 9. The method of claim 7, wherein the hole passes through the lower layer and is a through hole.
 10. The method of claim 7, wherein an adhesive is injected into the hole and shear stresses on the vertical members are transferred to the pin via the adhesive.
 11. The method of claim 1, wherein the hole is a-through hole and the adhesive is provided in excess such that a blob of adhesive is formed beyond the farther surface from a point of injection.
 12. The method of claim 1, wherein a plate is threaded around an end of the pin.
 13. The method of claim 1, wherein the hole is drilled from below and passes through the vertical member and into an upper layer covering the vertical member.
 14. The method of claim 1, wherein the structure comprises a lower layer and the hole is drilled from below, through the lower layer and into the vertical member.
 15. The method of claim 14 wherein the hole is drilled into an upper layer.
 16. The method of claim 14 wherein the hole is a through hole, drilled through the upper layer.
 17. The method of claim 1 further comprising threading a protruding end of the reinforcing pin through a metal plate and locking in place.
 18. The method of claim 17 wherein locking comprises welding the pin to the plate.
 19. The method of claim 17 wherein locking comprises, bending over a protruding end of the vertical pin.
 20. The method of claim 17 wherein the protruding end of the pin is threaded and locking comprises applying a bolt onto the bar.
 21. The method of claim 1 further comprising a preliminary step of locating the vertical member.
 22. The method of claim 21 wherein locating the vertical member is selected from the list of visible observance, distance measurement, infra red emittance mapping, vibration mapping and drilling exploratory holes.
 23. A retro-reinforced waffle ceiling structure comprising substantially vertical pins passing through vertical members and at least one external layer of concrete; the pin coupled to the vertical member to combat shear stresses in the vertical member.
 24. The retro-reinforced waffle ceiling structure of claim 23, wherein the at least one external layer of concrete includes an upper floor covering the vertical member.
 25. The retro-reinforced waffle ceiling structure of claim 23, wherein the at least one external layer of concrete includes a lower layer contacting the undersurface of the vertical member.
 26. The retro-reinforced waffle ceiling structure of claim 23, wherein the at least one external layer comprises reinforced concrete.
 27. The retro-reinforced waffle ceiling structure of claim 23, wherein the substantially vertical pin comprises a reinforcement bar of mild steel with ribbing coupled to the vertical member by an epoxy.
 28. The retro-reinforced waffle ceiling structure of claim 23, wherein a metal plate is positioned over a protruding end of the vertical pin and either the pin is bent over to engage the plate, the bar is welded to the plate or the bar is threaded and a nut is threaded onto the thread. 